Question: Integrate error wrong number(type) of arguments

i want to integrate dbeta at the bottom of the following code, however, it said wrong number of argument. Why ? how to correct it the to integrate it successfully?

Af := ft + f1*dX + f2*dv + 1/2*f11*dXt + 1/2*f22*dvt + f12*dXvt;
Af := subs(dX = (miu - v/2)*dt, Af);
Af := subs(dv = a*(b - v)*dt, Af);
Af := subs( dXt = v*dt, Af);
Af := subs( dvt = v*(rho^2)*dt, Af);
Af := subs( dXvt = rho*p*v*dt, Af);

Af := subs( ft = (dalpha*y + dbeta)*f, Af);
Af := subs( f1 = i*theta*f, Af);
Af := subs( f2 = alpha*f, Af);
Af := subs( f11 = -(theta^2)*f, Af);
Af := subs( f22 = (alpha^2)*f, Af);
Af := subs( f12 = i*theta*alpha*f, Af);

Af := collect(Af, [f]);
Af := Af/f;
Af := subs( v = y, Af);
Af := subs( dt = 1, Af);
Af := collect(Af, [y, alpha]);

eq1 := isolate( (1/2)*alpha^2*rho^2+(-a+i*theta*rho*p)*alpha-(1/2)*i*theta+dalpha-(1/2)*theta^2, dalpha);
eq1 := collect( eq1, [alpha^2, alpha]);

A = -(1/2)*rho^2;
B = a-i*theta*rho*p;
C = (1/2)*i*theta+(1/2)*theta^2;

motion := diff(alpha(t), t) = A*alpha(t) + B*alpha(t)^2 + C;
sol := dsolve(motion);

sol := subs( A = -(1/2)*rho^2, sol);
sol := subs( B = a-i*theta*rho*p, sol);
sol := subs( C = (1/2)*i*theta+(1/2)*theta^2, sol);

dbeta := simplify(-i*theta*miu-a*b*sol);
beta := int(dbeta, t)