Unable to add secondary eSIM on iPhone 13 Pro Max

What model iPhone? If the particular iPhone has two SIM slots, then it has no eSIM.

Settings > General > About > tap on the Model Number to get the A model number.

Please post the A model number here.

A-chaudhary wrote:

iPhone 13pro max

model A2643 (MLLD3B/A)

That "global" model has one SIM slot, and should have eSIM support.

The EID for the iPhone should show in Settings > General > About

If the EID and support for eSIM is not showing, and if the iPhone is not carrier locked, then try a factory reset, then contact Apple and have them take a look at the iPhone.

Here is how to: Restore your iPhone, iPad, or iPod to factory settings - Apple Support

A-chaudhary wrote:

I just have SEID and MEID

Let me know if any of these will work, does my phone have Esim

That that model shows a “front SIM” and a “back SIM” means it is a model intended for China mainland, Hong Kong, or Macao, and thus does not have eSIM.

Why a dual-SIM model is being identified as A2643 MLLD3B/A is unclear.