diff --git a/lib/sim_repo.rb b/lib/sim_repo.rb
index 599ad081023a858cf374801d4eef43524e52269d..994d11f79f64cb3aa73fbb9d90b26c15ada80fe5 100644
--- a/lib/sim_repo.rb
+++ b/lib/sim_repo.rb
@@ -43,7 +43,7 @@ class SIMRepo
 		iccid = sim.is_a?(String) ? sim : sim.iccid
 
 		req("line/#{iccid}/refill").apost(
-			head: KEEPGO_HEADERS,
+			head: KEEPGO_HEADERS.merge("Content-Type" => "application/json"),
 			body: kwargs.to_json
 		).then { |req| JSON.parse(req.response) }
 	end