iOS Mail app switches aliases back to hotmail.com

Hi

i recently created an outlook alias for my hotmail account and made it the primary account name under Microsoft acxoutns

now when I go and set it up on my iPhone, Enter the outlook.com.au alias, it sets it up but then switches it back to hotmail.com

From also shows as sending from hotmail .com

anyone has this issue??

would love to get this sorted rather than use thenOutlook app seperately

thanks

varun