Reciprocation is being established.
He has replied quicker to my texts on two occasions when I've said "Hmm?" or chastised him for losing attention during a simple exchange.

Particularly in the reciprocation stage I think a Dom can double text to remind a sub that we expect something from them.

Assertive, non-needy is the basis.

But how do we quantify the extra leg room?

"Okay, I understand. If you do want to pursue it I'll pay for coffee 👍"

Feels like asking a little too much investment with the phone call. Start with a short reopener. Something funny, or passive

When she says "Same thing as u" just reply "FWB?", then leave the ball in her court (up to few days)