The problem may be that you are incorrectly trying to give the
p sound its full value with a little puff of air at the end. In combination with a following
t, the
p should be little more than a closing of the lips. You will not hear a full
p.
Say strap as stra with nothing more than a closing of the lips for the p part. Don't pronounce the p. Suppose that + means "Close your mouth quickly". Now say stra+, stra+, stra+.
When you can do that well, just add the t (stra+t) and then add the rest (stra+t for cash).
There is little difference between strat for and strapt for. The only difference is that your lips close between the a and the t. Just the closing of the lips is enough to suggest a p. Don't attempt to make the p any more prominent by trying to give a puff of air or anything like that. Say stra+t for cash.
(I assume the phrase for cash is not the problem.)
CJ