No alternatives and here's the Councils announcement: https://www.richmond.gov.uk/services/parking/parking_machine...

Some have extended to non-residential areas. One of the biggest parking apps says this:

Q: "I have no network coverage and need to park?"

A: "Move quickly to an area with better network coverage and complete your parking transaction with PayByPhone... Pay for your parking via other methods such as PayPoint or via the Pay & Display machine where available"

Reference: https://support.paybyphone.co.uk/hc/en-gb/articles/360010478...

FYI 'Pay and Display' are the parking meters being removed, 'PayPoint' might be in SOME convenience stores/shops. But if you know London these can be 20-30 mins walk or none there are all at your parking destination. Good luck attending an appointment during work lunch times!