ESIC registration, is it mandatory if there is no employee with salary less than 21,000 pm

Hi Experts,
It would be great if some one can guide me.
I run a company with 28 employees as on date in Pune, Maharashtra. All have gross salary above 21,000/ pm. All are covered under EPF.
Now one of my client is insisting on having ESIC registration.
Following are my questions
1. Without having any employees under 21k gross salary, is it mandatory to have ESIC registration.
2. If it is mandatory, online ESIC employer registration portal is not allowing to enter ' any number less than 20'
looking for help/advise
thanks

Referrring to your mail, you have stated that all your employees have gross salary above 21000/-
but they are covered under PF. PF salary ceiling is only 15000/-. Those employees whose salary
is upto Rs.15000/- could be covered under PF.
Currently, ESI is applicable to only establishments (Factory, Shop, Commercial establishments, Educational Institutions, Hospitals,Laboratories) where minimum 10 employees have worked for minimum one day. Now new Labour Code is approved by President of India, and also published in Official Gazette, dated 29th Sept 2020.
As per new Code, even if only one employee is working in establishments where hazardous or life threatening work is carried out, ESI conditions shall be applicable.
While considering “wages” for making contributions, the components such as House rent allowance, overtime allowance, commission, travel allowance are excluded, as per new Code