import re
 
regex = r"^INV\+(?:[^+\n]*\+){4}(\d{8})"
 
test_str = ("UNA:+,? '\n"
	"UNB+UNOC:3+000000000+000000000+20190801:1115+00001+DDMP190001'\n"
	"UNH+00001+BRKE:01+00+0'\n"
	"INV+ED Format 1+Brustkrebs+19880117+E000000001+20080702+++1+0'\n"
	"FAL+087897044+0000000++Trägername+000000000+0+20080702++1+++J+N+N+N+N+N+++0'\n"
	"INL+181095200+385762115+++0'\n"
	"BEE+20080702++++0'\n"
	"BAA+++J+J++++++J+++++++J++0'\n"
	"BBA++++++++J++++++J+J++++++J+++++J+++J+J++++++++J+0'\n"
	"BHP+J+++++J+++++J+++++0'\n"
	"BLA+++J+++++++++0'\n"
	"BFA++++++++++++J++0'\n"
	"BSA++J+++J+J+++0'\n"
	"BAT+20190801+0'\n"
	"DAT+20080702++++0'\n"
	"UNT+000014+00001'\n"
	"UNZ+00001+00001'\n\n")
 
matches = re.search(regex, test_str, re.MULTILINE)
 
if matches:
	print(matches.group(1))

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