Deduction for expats to pay for GOSI

Dear sir,

I am from India and I am doing software developer job in Bahrain; joined in Bahrain 18-03-2019.

In the offer letter, they didn't mention any deductions but in this month, i.e. April 2019, they deducted from my salary 1%.

The following rule, in which year onwards was it implemented in Bahrain?

For the expatriates, 4% of the full salary including the allowances (3% being the employer share, and 1% being the expat employee share).

Thank you and have a nice evening.

Best regards,

S.