A question about write BAPI with delphi~

Dear gulus:

I have declare a function in SAP, the function have a import parameters:P_MATNR, and the P_MATNR's type is MATNR,

when i call the function in delphi,

and export the parameters like following code:

Funct.exports('P_MATNR'):= 'ABS00221+GPG00103' ,

when i run the code, it show an error and say "Type is not match."类型不匹配。

why? who can help me ? thanks in advance.