Hi there.
Thank you for reaching out to us via the forum.
The error "Invalid URL for MYOB authorization" suggests the URL you are using to Authorise isn't correct.
Before clicking "Allow Access" the system should give you the option to login to your MY.MYOB account (developer registration), the URL for sending this information is:
https://secure.myob.com/oauth2/account/authorize?client_id={{api_key}}&redirect_uri={{redirect_url}}&response_type=code&scope=CompanyFile la.global
After clicking "Allow Access" the system will look for your "Redirect URI" in order to navigate back to your application.
In your setup, we may want to look at "redirect URI" header and make sure this is the correct address.
The suport note below will take you through each step.
https://apisupport.myob.com/hc/en-us/articles/360001459455-How-to-Complete-End-User-Authentication-with-OAuth2-0
Also this support note shows video of the Authorisation being completed using the POSTMAN software, you may be able to reference the steps with your own app.
https://developer.myob.com/api/accountright/accountright-postman-collection/
If you continue to have trouble, create a support ticket using the link below and we will investigate further.
https://developer.myob.com/contact/
Kind regards
