Yeah, the issue is more that there is substantial friction in paying any amount of money, especially in poorer countries with no access to e.g. banking or payment cards. I'm sure no one here, and few people even in comparatively poorer countries, would object if Signal/their messenger of choice cost 0.60$ per year to use. The problem is that making the service have a ~1$/yr price tag (as WhatsApp once had) is itself a barrier to a huge portion of the target audience.
In Pakistan at least, sometimes you can donate to charity etc by texting a special number [1]. That subtracts some fixed amount from your prepaid mobile balance (which the vast majority of people use) or adds to your postpaid bill. I imagine its possible for some business to charge customers this way as well.
Then again, instant C2C and C2B digital payments using mobile phones is growing extremely fast in most of the global south.
