Cannot make Google Play purchases over mobile data

I am currently unable to purchase apps/games within the Play Store. This includes in-app purchases.
I receive this server error every single time. I can, however, make purchases over WiFi without receiving the error.
Does anyone know how I can fix this?

I am using a SM-G935F with a T-Mobile USA sim card.
The build version of my Play Store is 6.9.15

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