My custom fluid cannot be placed in the cauldron

Good morning. I need help - these are my beginnings in this program, so please be understanding, I would also like to point out that I tried to search the forum for answers that interest me. Unfortunately, I did not find a satisfactory answer to my problem - and the matter may be very prosaic and easy.

I created a custom fluid that meets my expectations, but it cannot be used in cauldron.
I see that it has the appropriate tag -minecraft:water- but when I try to put it in the cauldron it just spills around

As I wrote, maybe it's my childish mistake - please tell me what I did wrong