Issue in dynamic action

Dear expert!

Now, I'm getting some issues about dynamic action.

- The first, I write program with content the following:

REPORT ZHSENDMAIL.

• Data Declarations

DATA: lt_mailsubject TYPE sodocchgi1.

DATA: lt_mailrecipients TYPE STANDARD TABLE OF somlrec90 WITH HEADER LINE.

DATA: lt_mailtxt TYPE STANDARD TABLE OF soli WITH HEADER LINE.

PERFORM sendmail.

FORM sendmail.

• Recipients

lt_mailrecipients-rec_type = 'U'.

lt_mailrecipients-receiver = 'email'.

APPEND lt_mailrecipients .

CLEAR lt_mailrecipients .

• Subject.

lt_mailsubject-obj_name = 'TEST'.

lt_mailsubject-obj_langu = sy-langu.

lt_mailsubject-obj_descr = 'Mail Subject'.

• Mail Contents

lt_mailtxt = 'This is a test mail'.

APPEND lt_mailtxt. CLEAR lt_mailtxt.

• Send Mail

CALL FUNCTION 'SO_NEW_DOCUMENT_SEND_API1'

EXPORTING

document_data = lt_mailsubject

TABLES

object_content = lt_mailtxt

receivers = lt_mailrecipients

EXCEPTIONS

too_many_receivers = 1

document_not_sent = 2

document_type_not_exist = 3

operation_no_authorization = 4

parameter_error = 5

x_error = 6

enqueue_error = 7

OTHERS = 8.

IF sy-subrc EQ 0.

COMMIT WORK.

• Push mail out from SAP outbox

SUBMIT rsconn01 WITH mode = 'INT' AND RETURN.

ENDIF.

ENDFORM.

- Second, in dynamic action with infotype 0002, I create new entry the following:

Sty. Field N FC No S Variable function part

FATXT 06 1 F sendmail(ZHsendmail)

After that, when I change value for field FATXT then Routine 'sendmail' doesn't perform.

why?

Help me, please!

Best regards Huy!