[Idiom] how to decribe the integer multiple ?

[kevin_von]

When putting more credit into a mobile phone account or a public travel card, I oftem meet such kind of instruction by the that you can only add the amount of 50, 100, 150, 200 or the like .

My question is that how to decribe this kind of instruction in a formal way.

You can only put the USD50 or its integer multiple ?

One of my friend who is a greenhand selling the metallic sheet to overseas market also has meet this quesiton because the width of his products may be 100mm, 200mm, 300mm etc.
But he is confused on how to express this in a formal way instead of listing

[2006]

Originally Posted by kevin_von

When putting more credit into a mobile phone account or a public travel card, I oftem meet such kind of instruction by the that you can only add the amount of 50, 100, 150, 200 or the like .
You can say 'You can add 50 or multiples of 50 to a maximum of ___.'
or
'You can add multiples of 50 from 50 to a maximum of ___.'
My question is that how to decribe this kind of instruction in a formal way.

You can only put the USD50 or its integer multiple ? as above

One of my friend who is a greenhand selling the metallic sheet to overseas market also has meet this quesiton because the width of his products may be 100mm, 200mm, 300mm etc. This product comes in sizes of 100 mm and multiples of 100 mm to a maximum of ___ mm.'
But he is confused on how to express this in a formal way instead of listing

2006