Static shipping is calculated once, using the stores base address. If the shipping can be calculated that way, it can be used. If it depends on the address, it cannot. But using Bring should not break the system anyway.
To diagnose 503-type errors you will need to look at the fatal-errors log, not the vipps log, however. these lines are concerning:
2023-09-05T07:13:25+00:00 INFO Feil under henting av kundedata i Vipps fraktdetaljer-callback: Syntax error
2023-09-05T07:13:25+00:00 INFO Dataene som ble sendt var
2023-09-05T07:13:25+00:00 INFO
2023-09-05T07:13:25+00:00 INFO Fant ingen fraktmetoder for Vipps Hurtigkasse - ordren vil mislykkes
This will cause the same symptoms as the one you described, but this is not the 503 error. It seems here that it was not possible to decode the customer data sent by Vipps, and that reason for this is that the contents were empty.
$raw_post = @file_get_contents( 'php://input' );
$result = @json_decode($raw_post,true);
Now, this should only be input if either there is a redirect (that is, the original POST gets a 301/302) or if something *else* reads from php://input first. So you will also need to see if the shipping callbacks get redirected; you *probably* won’t have a plugin that reads from stdin.
In the error logs you sent, there were a lot of instances of this:
PHP Fatal error: Uncaught Error: Unknown named parameter $tasks_meta_id
This should not really affect the rest of the system, because it occurs in the action scheduler/cron subsystem, but it is a symptom that you have at least one plugin (or something in the theme) which is not compatible with PHP 8 – you can google the error for more info.
Even if these have nothing to do with the problem at hands you should try to find out which plugin causes this, and update or replace it.
