1) You have a little naming issue (but I suppose you've solved that on your end, since you don't have a naming error). Notice that you've defined the PROC as "CALCULATION" (no commas = all capital letters) but is calling "claims.dev_test/calculation".
2) you're overwritting the output (result_value) variable when you (re)declare it.
Just delete the following line:
declare result_value decimal(20,4);
And your code should work fine.
Best,
Henrique.