I will keep a number either 11 digits or 15 digits or 16 digits

[Kal_Lam]

@mdnurnabi, maybe this post discussed previously should help you solve your issue as outlined by @wroos:

Restrict for Entering 10, 13 OR 17 digit number only

Try changing the above to either of the two Option 1 regex(., ‘^[0-9]{10}$’) or regex(., ‘^[0-9]{13}$’) or regex(., ‘^[0-9]{17}$’) Option 2 regex(., ‘^([0-9]{10}|[0-9]{13}|[0-9]{17})$’)