This question seems to interest all business travelers in the EU.
But I will ask for it from my personal point of view. I work in a university of the EU (Germany). Today, we received an e – mail stating that we had to apply for an A1 form for social security contributions if we went to another EU country for any type of business trip.
A quick search on the web indicates that several German health insurance companies share this interpretation of the European directive  and big companies like KPMG . In addition, their interpretation suggests that this rule applies to all EU citizens who work in an EU country and who will travel to another EU country for No matter what type of business trip.
After rapid skimming of the EU regulation 987/2009 For me personally, all this seems to make sense for detachments at another university, research center or company. But not to attend conferences, give a short lecture or have a short meeting.
Is the first interpretation that an A1 form is required for any small business trip really correct? How is this treated in other EU countries?
 https://www.tk.de/firmenkunden/service/versicherung/tk-service-ausland/haeufige-fragen-zum-a1-2038394 (german)
 https://home.kpmg/xx/en/home/insights/2018/08/flash-alert-2018-115.html (English)
 https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32009R0987&from=en (English)