You probably require a 'passive' type flux which does not leave corrosive residues. This Orange flux is resin based and will do the job you require of it (or other similar product).
The only proviso is that you must ensure both parts must be very clean and degreased. You may already know that it will be an advantage to 'tin' both parts separately first and then solder them together.
If using cored flux solder, you may still have issues if the cored flux contains an 'active' ingredient.
I'm sure more experienced members or retailers can add to, or correct this opinion. I have always had good results from this product with no interest or link to the suppliers.