Don't forget, these options have been around for a while but no one seems to like doing it. Arriva tickets can be bought at Paypoint and Payzone. Merseyside and Manchester offer tickets via these stores but most people tend not to buy tickets via these outlets. Instead preferring to go direct and buy on the bus or using official apps.
When West Yorkshire's Metro launched the MCard there was no app or online purchases. They could be topped up with tickets at Bus Stations when open and at Payzones.
However, the online information about opening times was wrong for most stores. I used to arrive in Leeds from time to time on a long distance service and wanted to get a weekly ticket including the train and bus home from Leeds. I visited 4 different stores that were marked as open at various times to discover they weren't. I had to make my own list of when they were open. Complaining to PayZone had little effect.
My local Payzone store was a 10 minute walk from my home. I never managed to put a ticket on the MCard - sometimes they reported the machine wasn't working, or the person who knew how to use it wasn't there. After 2 years of complaints Metro proposed a solution - removing my local stpre from the list for those searching for just that function! I can see they they're not a popular option.
Being able to buy on the app was a godsend, especially when they finally added combined train and bus tickets (bus only were added fairly quickly) - and now you can choose to use your phone or a card.