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Your LimeSurvey version: Version 6.3.8+231204 
Own server or LimeSurvey hosting: University server
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(Write here your question/remark)
Hello, I would like to know if it's possible to format the content of the invitation email in the API request "mail_registered_participants" that I want to send to participants in my survey. Currently, I can send a generic invitation email using the API, but I would like to make it more specific. Since it's a longitudinal study, my goal is to create a script that updates the participant list and automatically sends invitation emails. What is the name of the parameter I should provide for this? Unfortunately, I've searched a lot and don't know how to do it.Thank you very much for your help.

What do you mean by "more specific"

You can use (for example) attributes in email templates, then adapt text according to such attribute.
 

Thank you, Denis, for the response.
I mean that I want to personalize my invitation email with a message addressed to the respondents, including explanations on how to complete the survey.
Here is the script I use to automate the sending of invitation emails.
I use RStudio with the "httr" package.      # Paramètre des conditions
overrideAllConditions <- list('tid = 4130')

# Construire la requête pour appeler la fonction mail_registered_participants
mailParticipantsRequest <- POST(
  rpcEndpoint,
  body = list(
    method = "mail_registered_participants",
    params = list(
      sSessionKey = key,
      iSurveyID = IDTokenORIG,
      overrideAllConditions = overrideAllConditions
    ),
    id = 1
  ),
  encode = "json"
)

# Exécuter la requête et obtenir la réponse
mailParticipantsResponse <- content(mailParticipantsRequest)

# Vérifier la réponse et traiter les résultats
if (!is.null(mailParticipantsResponse$error) && length(mailParticipantsResponse$error) > 0) {
  print(paste("Erreur lors de l'envoi des e-mails aux participants enregistrés :", mailParticipantsResponse$error[1]))
} else {
  print("E-mails envoyés avec succès aux participants enregistrés.")
  print("Informations sur l'action :")
  print(mailParticipantsResponse$result)
}

Thank you for the time you dedicate to addressing my issue
 

I think you can't updateb the content of the email when using API.

BUT : using attribute

Or directly Where the sentence are in the attribute

attribute can be set in api.limesurvey.org/classes/remotecontrol...hod_add_participants

or updated in api.limesurvey.org/classes/remotecontrol...rticipant_properties

Hello Denis,
I finally figured out what wasn't working. In fact, I wasn't using the right query, so the email I was sending was the notification to the administrator used for survey follow-up reminders to the administrator (query: mail_registered_participants). Whereas, in fact, I needed the "invite_participants" query, which allowed me to automate the sending of the email I had already prepared on the LimeSurvey platform and which included the use of "attributes." Anyway, I just wanted to thank you for taking the time to respond to me.