Form with checkbox questions can't be submitted without 400 error

[gerbsen]

Describe the bug
I can't submit a form without an HTTP 400 Error.

To Reproduce
Steps to reproduce the behavior:

1. Create a new form with one checkbox question (seems to be a problem too for radio and dropdown)
2. Fill out the form
3. Submit
4. See error and screenshot: There was an error submitting the form: Answer "46" for question "Checkbox question" is not a valid option. (the number always changes)

Expected behavior
Each selection should be saved to XLS file without any error.

Screenshots

Nextcloud (please complete the following information):

• Nextcloud-Version: 32.0.3
• Forms-Version: 5.2.3
• Safari: 26.2 (but also other browsers)

Browser log

curl 'https://cloud.xxxxxxxxxx.de/ocs/v2.php/apps/forms/api/v3/forms/12/submissions' \
-X 'POST' \
-H 'Content-Type: application/json' \
-H 'Pragma: no-cache' \
-H 'Accept: application/json, text/plain, */*' \
-H 'Sec-Fetch-Site: same-origin' \
-H 'Accept-Language: en-GB,en;q=0.9' \
-H 'Cache-Control: no-cache' \
-H 'Sec-Fetch-Mode: cors' \
-H 'Accept-Encoding: gzip, deflate, br' \
-H 'Origin: https://cloud.xxxxxxxxxx.de' \
-H 'Content-Length: 40' \
-H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/26.2 Safari/605.1.15' \
-H 'Referer: https://cloud.xxxxxxxxxx.de/apps/forms/qPiKgZk7DWi69C6s/submit' \
... // some stuff removed not sure if security relevant
--data-raw '{"answers":{"52":["46"]},"shareHash":""}'

Response:

{
    "ocs": {
        "meta": {
            "status": "failure",
            "statuscode": 400,
            "message": "Answer \"46\" for question \"Checkbox question\" is not a valid option."
        },
        "data": []
    }
}

[Chartman123]

@gerbsen thanks for reporting, however, I cannot reproduce this. So probably some problem specific to your instance. Could you please verify in the browser dev tools inside the network tab, which data is loaded for the form when you open it? you should then see the question with the nested options and the corresponding IDs.

[gerbsen]

I hope this is what you mean:

{
    "ocs": {
        "meta": {
            "status": "ok",
            "statuscode": 200,
            "message": "OK"
        },
        "data": {
            "id": 12,
            "hash": "qPiKgZk7DWi69C6s",
            "title": "A simple form",
            "description": "which runs into http 400 for each select element",
            "ownerId": "admin",
            "fileId": null,
            "fileFormat": null,
            "created": 1768424031,
            "access": {
                "permitAllUsers": false,
                "showToAllUsers": false
            },
            "expires": 0,
            "isAnonymous": false,
            "submitMultiple": false,
            "allowEditSubmissions": false,
            "showExpiration": false,
            "lastUpdated": 1768474519,
            "submissionMessage": null,
            "state": 0,
            "lockedBy": "admin",
            "lockedUntil": 1768475419,
            "questions": [
                {
                    "id": 52,
                    "formId": 12,
                    "order": 1,
                    "type": "multiple",
                    "isRequired": false,
                    "text": "Checkbox question",
                    "name": "",
                    "description": "description foo.. ",
                    "extraSettings": [],
                    "options": [
                        {
                            "id": 46,
                            "questionId": 52,
                            "order": 1,
                            "text": "one"
                        },
                        {
                            "id": 47,
                            "questionId": 52,
                            "order": 2,
                            "text": "two"
                        },
                        {
                            "id": 48,
                            "questionId": 52,
                            "order": 3,
                            "text": "three"
                        }
                    ],
                    "accept": []
                }
            ],
            "shares": [
                {
                    "id": 9,
                    "formId": 12,
                    "shareType": 3,
                    "shareWith": "gW8BXZZ7sfFfsbXAeDaLPzGL",
                    "permissions": [
                        "submit"
                    ],
                    "displayName": ""
                }
            ],
            "permissions": [
                "edit",
                "embed",
                "results",
                "results_delete",
                "submit"
            ],
            "canSubmit": true,
            "submissionCount": 3
        }
    }
}

[Chartman123]

@gerbsen yes, thanks :) But there's nothing suspicious there... All IDs in question are correctly there.

Do you get the error as logged in user or via the public share?

[Chartman123]

@susnux the error is thrown here:

forms/lib/Service/SubmissionService.php

Lines 461 to 464 in 569905f

	// Search corresponding option, return false if non-existent
	elseif (!in_array($answer, array_column($question['options'], 'id'))) {
	throw new \InvalidArgumentException(sprintf('Answer "%s" for question "%s" is not a valid option.', $answer, $question['text']));
	}

Do you have an idea why this could fail if the IDs are correct?

[susnux]

Do you have an idea why this could fail if the IDs are correct?

Are the type correct? so is $answer and $questions['options']['id'] of the same type?
I can image there is some string vs int thing.

[gerbsen]

@gerbsen yes, thanks :) But there's nothing suspicious there... All IDs in question are correctly there.

Do you get the error as logged in user or via the public share?

I get this error as logged in user as well as with an anonymous link. As anonymous users I can't find the ocs json.

[gerbsen]

Do you have an idea why this could fail if the IDs are correct?

Are the type correct? so is $answer and $questions['options']['id'] of the same type? I can image there is some string vs int thing.

Is there any way for me to debug this?

[Chartman123]

Does it happen with every form or only with this special one? You could try to set your Nextcloud instance to debug logging and see if there are more interesting logs in the server logging in the admin area.

Also: what are your server specs? PHP version, used database?

[gerbsen]

This happens with every form where I select some option form element. I can submit a form where I leave the checkbox question empty. I run a docker compose setup. DB-type: mysql, Version: 10.6.24

Version: 8.3.28

Memory limit: 512 MB

Max execution time: 10800

Upload max size: 10 GB

OPcache Revalidate Frequency: 60

Extensions: Core, date, libxml, openssl, pcre, sqlite3, zlib, ctype, curl, dom, fileinfo, filter, hash, iconv, json, mbstring, SPL, session, PDO, pdo_sqlite, bz2, posix, random, readline, Reflection, standard, SimpleXML, tokenizer, xml, xmlreader, xmlwriter, mysqlnd, cgi-fcgi, apcu, bcmath, Phar, exif, gd, gmp, imagick, intl, ldap, pcntl, pdo_mysql, pdo_pgsql, redis, smbclient, sodium, sysvsem, zip, snuffleupagus, libsmbclient, Zend OPcache

I switch to debug logging and found this:

{"reqId":"1tOFCRyCEYOeZsp7nlcF","level":0,"time":"2026-01-15T14:08:28+00:00","remoteAddr":"X.X.X.X","user":"admin","app":"forms","method":"POST","url":"/ocs/v2.php/apps/forms/api/v3/forms/12/submissions","message":"Inserting submission: formId: 12, answers: {\"52\":[\"46\"]}, shareHash: ","userAgent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/26.2 Safari/605.1.15","version":"32.0.3.2","data":{"app":"forms"}}

Looks to me like a string != int comparison, just as @susnux suggested?

[Chartman123]

You also have the escaped quotes in the original error message... This is kind of strange. Not sure where this is coming from. In my JSON, that is sent to the server when I submit a form with a checkbox question, it looks just the same way like what you have posted in your curl call in the OP. So the escaping must happen on the server...

Payload when I test the submission on my instance: {"answers":{"1234":["5678"]},"shareHash":""}

[gerbsen]

Alright, I now have var_dump the values from forms/lib/Service/SubmissionService.php

Array
(
    [answer] => string(2) "46"
    [question] => Array
    (
        [id] => int(52)
        [formId] => int(12)
        [order] => int(1)
        [type] => string(8) "multiple"
        [isRequired] => bool(false)
        [text] => string(17) "Checkbox question"
        [name] => string(0) ""
        [description] => string(18) "description foo.. "
        [extraSettings] => Array
        (
        )
        [options] => Array
        (
            [0] => Array
            (
                [id] => int(46)
                [questionId] => int(52)
                [order] => int(1)
                [text] => string(3) "one"
            )
            [1] => Array
            (
                [id] => int(47)
                [questionId] => int(52)
                [order] => int(2)
                [text] => string(3) "two"
            )
            [2] => Array
            (
                [id] => int(48)
                [questionId] => int(52)
                [order] => int(3)
                [text] => string(5) "three"
            )
        )
        [accept] => Array
        (
        )
    )
    [valid_options] => Array
    (
        [0] => int(46)
        [1] => int(47)
        [2] => int(48)
    )
)

Could this be related to my NGINX reverse proxy? I remember something similar for a java server a while back. I have no idea about php, is there something else which can change the parameter types?