How Do I resolve "Illuminate\Queue\InvalidPayloadException: Unable to JSON encode payload. Error code: 5" - laravel-7

Question

Trying out the queue system for a better user upload experience with Laravel-Excel.
.env was been changed from 'sync' to 'database' and migrations run. All the necessary use statements are in place yet the error above persists.
The exact error happens here:
Illuminate\Queue\Queue.php:97
$payload = json_encode($this->createPayloadArray($job, $queue, $data));
if (JSON_ERROR_NONE !== json_last_error()) {
throw new InvalidPayloadException(
If I drop ShouldQueue, the file imports perfectly in-session (large file so long wait period for user.)
I've read many stackoverflow, github etc comments on this but I don't have the technical skills to deep-dive to fix my particular situation (most of them speak of UTF-8 but I don't if that's an issue here; I changed the excel save format to UTF-8 but it didn't fix it.)
Ps. Whilst running the migration, I got the error:
SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes (SQL: alter table `jobs` add index `jobs_queue_index`(`queue`))
I bypassed by dropping the 'add index'; so my jobs table is not indexed on queue but I don't feel this is the cause.

Answer 1

One thing you can do when looking into json_encode() errors is use the json_last_error_msg() function, which will give you a bit more of a readable error message.
In your case you're getting a '5' back, which is the JSON_ERROR_UTF8 error code. The error message back for this is a slightly more informative one:
'Malformed UTF-8 characters, possibly incorrectly encoded'
So we know it's encountering non-UTF-8 characters, even though you're saving the file specifically with UTF-8 encoding. At first glance you might think you need to convert the encoding yourself in code (like this answer), but in this case, I don't think that'll help. For Laravel-Excel, this seems to be a limitation of trying to queue-read .xls files - from the Laravel-Excel docs:
You currently cannot queue xls imports. PhpSpreadsheet's Xls reader contains some non-utf8 characters, which makes it impossible to queue.
In this case you might be stuck with a slow, non-queueable option, or need to convert your spreadsheet into a queueable format e.g. .csv.
The key length error on running the migration is unrelated. It has been around for a while and is a side-effect of using an older version of MySQL/MariaDB. Check out this answer and the Laravel documentation around index lengths - you need to add this to your AppServiceProvider::boot() method:
Schema::defaultStringLength(191);