In some cases, Bitcoin acceptance requires the use of 3rd party Companion Apps that generate invoices on behalf of the merchant. Sometimes the merchant is not even aware you are paying with bitcoin.
If a Companion App is required then the following tags should be used:
payment:lightning:companion_app_required=yes
payment:lightning:companion_app_url:https://app-url-com
Here is a list of known Companion Apps:
If a merchant supports bitcoin natively and via a companion app then most clients will only display the native payment methods.
