I’m in Europe as well however my country hasn’t been affected by this change (whew). I make all my sales like you do via messenger. I suggest you optimize for engagement or reach and put a phone number in your
captions. Repeat the phone number number 2-3 times in the ad so people can easily spot it, use emojis. Add the number on your page contact, Instagram bio and on ad images as well. Make a little template on Canva that you can always use.
Make it clear that they can text via WhatsApp or Viber, this is how I would go for it. But if you can take calls then sure do that as well.
I suggest you try this out for at least a week, different creatives etc. Good luck!