[1] Seventeen days later, he made his debut against Arminia Hannover after being named in the starting line-up and scored his side's second goal during a 3–3 home draw.

[4] Fourteen days later, he made his debut in a 3–1 away defeat against Tirana after coming on as a substitute in the 41st minute in place of injured Gjergji Muzaka.

[16] On 4 October 2018, Muja received a call-up from Kosovo U21 for the 2019 UEFA European Under-21 Championship qualification match against Israel U21,[17] and made his debut after coming on as a substitute at 64th minute in place of Muharrem Jashari.

[21] Head of the Department of Public Relations of the Albanian Football Association, Andi Verçani confirmed two days later through an interview for Koha Ditore that Muja will be called up by Albania in September 2023 for the UEFA Euro 2024 qualifying matches against Czech Republic and Poland.

[22] On 1 September 2023, he formalizes the decision and accept their call-up for the UEFA Euro 2024 qualifying matches against Czech Republic and Poland.