Hello my friend
I can not assure you 100% Whether it is magnesium deficiency. But if that's the case here's what you can do
As a quick emergency corrective action, magnesium sulfate can be mixed with water and foliar sprayed. Magnesium sulfate is actually Epsom salt, and it is easy to get it online or in pharmacies. To prepare the foliar solution, dilute one tablespoon of Epsom salt in four liters of water. Then spray the solution on the leaves every three days, and spray them with clean water every 10 days to eliminate any accumulation of magnesium on the leaves.
May the strength be with you 💪