What's the verb form of 'deadbeat' in English? [duplicate]

Solution 1:

Another alternative would be renege:

to go back on a promise or commitment
_{from m-w.com}

This lacks the cultural slur of welsh/welch and is also widely used and understood. (Many of the example sentences at the M-W definition involve promises of payment, exactly as in your proposed sentence.)

Solution 2:

A common expression here in the US is to say someone stiffed someone else. It works for private loans or debts or even for defaulting on a formal loan, as in

"I had the money to repay the bank, then a gorgeous woman wanted me to take her to Cancun, so I decided to stiff the bank".

The expression is also used for tacit debts, for example,

"I was so embarrassed when my date stiffed the bartender last night"

(meaning, did not leave a tip).