The vast majority of declines are ‘user error’, where people research online first, then click through from a portal later expecting to be paid a commission. The BA e-store (along with all similar cash back portals) are very clear that theirs must be the first cookie with a track to the website you buy from - you agree to these T&C so can’t later argue otherwise! There’s a really simple solution - either use separate browsers, or delete cookies before starting your final purchase run.